This Recycled Concrete Structural Backfill technical note addresses structural integrity. General notes and a detail are provided.

The structural integrity of buried flexible structures is dependent upon both the strength of the flexible structure and the strength of the surrounding soils. The StormTech® Design Manual provides a list of “Acceptable Fill Materials” that have been found to provide proper structural support for StormTech chambers. Recycled, crushed concrete (also referred to as Reclaimed Concrete Material – RCM) may provide an excellent structural backfill but hardness and durability characteristics vary depending on the mix design. To qualify recycled, crushed concrete for a particular application, the consulting engineer may require hardness and durability testing. Similarly, natural limestone materials vary in hardness and durability depending on the source and in some cases, testing may be desirable.

The following are specifications that StormTech recommends for the acceptance of reclaimed crushed concrete based on criteria for structural integrity: The gradation shall meet AASHTO M43 gradations as listed in the “Acceptable Fill Materials Table” in the StormTech Design Manual. The material shall meet ASTM D2488 angular or subangular classification. Deleterious materials shall be limited to: a) maximum 20% reclaimed pavement materials and b)maximum 0.15% building materials. For material hardness – Maximum loss of 40% in the LA Abrasion test (AASHTO T96). Freeze-Thaw Resistance – Maximum 12% loss after 5 cycles in magnesium sulfate solution (AASHTO T104). The design shall be in accordance with the StormTech Design Manual and Installation shall be in accordance with the StormTech Installation Instructions.

A cross section of the StormTech Chamber system surrounded by foundation and embedment stone is provided.